rxrpc: Avoid using stack memory in SG lists in rxkad

rxkad uses stack memory in SG lists which would not work if stacks were
allocated from vmalloc memory.  In fact, in most cases this isn't even
necessary as the stack memory ends up getting copied over to kmalloc
memory.

This patch eliminates all the unnecessary stack memory uses by supplying
the final destination directly to the crypto API.  In two instances where a
temporary buffer is actually needed we also switch use a scratch area in
the rxrpc_call struct (only one DATA packet will be being secured or
verified at a time).

Finally there is no need to split a split-page buffer into two SG entries
so code dealing with that has been removed.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/ar-internal.h

@@ -141,17 +141,16 @@ struct rxrpc_security {
 	int (*init_connection_security)(struct rxrpc_connection *);
 
 	/* prime a connection's packet security */
-	void (*prime_packet_security)(struct rxrpc_connection *);
+	int (*prime_packet_security)(struct rxrpc_connection *);
 
 	/* impose security on a packet */
-	int (*secure_packet)(const struct rxrpc_call *,
+	int (*secure_packet)(struct rxrpc_call *,
 			     struct sk_buff *,
 			     size_t,
 			     void *);
 
 	/* verify the security on a received packet */
-	int (*verify_packet)(const struct rxrpc_call *, struct sk_buff *,
-			     u32 *);
+	int (*verify_packet)(struct rxrpc_call *, struct sk_buff *, u32 *);
 
 	/* issue a challenge */
 	int (*issue_challenge)(struct rxrpc_connection *);
@@ -399,6 +398,7 @@ struct rxrpc_call {
 	struct sk_buff_head	rx_oos_queue;	/* packets received out of sequence */
 	struct sk_buff		*tx_pending;	/* Tx socket buffer being filled */
 	wait_queue_head_t	tx_waitq;	/* wait for Tx window space to become available */
+	__be32			crypto_buf[2];	/* Temporary packet crypto buffer */
 	unsigned long		user_call_ID;	/* user-defined call ID */
 	unsigned long		creation_jif;	/* time of call creation */
 	unsigned long		flags;

net/rxrpc/conn_event.c

@@ -188,7 +188,10 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
 		if (ret < 0)
 			return ret;
 
-		conn->security->prime_packet_security(conn);
+		ret = conn->security->prime_packet_security(conn);
+		if (ret < 0)
+			return ret;
+
 		read_lock_bh(&conn->lock);
 		spin_lock(&conn->state_lock);
 

net/rxrpc/conn_object.c

@@ -138,7 +138,9 @@ rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
 	if (ret < 0)
 		goto error_1;
 
-	conn->security->prime_packet_security(conn);
+	ret = conn->security->prime_packet_security(conn);
+	if (ret < 0)
+		goto error_2;
 
 	write_lock(&rxrpc_connection_lock);
 	list_add_tail(&conn->link, &rxrpc_connections);
@@ -152,6 +154,8 @@ rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
 	_leave(" = %p", conn);
 	return conn;
 
+error_2:
+	conn->security->clear(conn);
 error_1:
 	rxrpc_put_client_connection_id(conn);
 error_0:

net/rxrpc/insecure.c

@@ -17,11 +17,12 @@ static int none_init_connection_security(struct rxrpc_connection *conn)
 	return 0;
 }
 
-static void none_prime_packet_security(struct rxrpc_connection *conn)
+static int none_prime_packet_security(struct rxrpc_connection *conn)
 {
+	return 0;
 }
 
-static int none_secure_packet(const struct rxrpc_call *call,
+static int none_secure_packet(struct rxrpc_call *call,
 			       struct sk_buff *skb,
 			       size_t data_size,
 			       void *sechdr)
@@ -29,7 +30,7 @@ static int none_secure_packet(const struct rxrpc_call *call,
 	return 0;
 }
 
-static int none_verify_packet(const struct rxrpc_call *call,
+static int none_verify_packet(struct rxrpc_call *call,
 			       struct sk_buff *skb,
 			       u32 *_abort_code)
 {